Ultraviolet (UV) radiation poses a serious threat to human health through its damaging effects on DNA. Such damage interferes with fundamental cellular processes, and can cause permanent changes to the DNA, leading to abnormal cell activity and clinical problems such as cancer. To counter the deleterious effects of UV radiation and other mutagenic agents, cells possess an array of DNA damage response and repair systems. Dysfunction of these systems is the root cause of a variety of DNA damage sensitivity disorders in humans. DNA repair in eukaryotic organisms is influenced by a family of highly conserved proteins called histones, which serve to structurally organize and functionally regulate DNA in the nucleus. This regulation is achieved in part by numerous histone post-translational modifications, which can influence the association of chromatin binding proteins, such as those involved in transcription, replication, and DNA repair. As suggested by their broad functionality, disruption of these modifications is associated with various mammalian developmental anomalies and cancer. We and others have previously found that a specific histone modification, methylation of lysine-79 in histone H3 (H3K79), is important for the response to DNA damage caused by UV radiation. Using the yeast Saccharomyces cerevisiae as a model system, we have shown that loss of this modification renders cells hypersensitive to UV radiation, with genetic evidence indicating that this modification acts through a variety of DNA damage response and repair pathways. Furthermore, we have evidence suggesting that specific H3K79 methylation states (i.e. the number of methyl groups attached to H3K79) play distinct roles in the response to UV damage. Based on our collective observations and those of others, we propose that UV radiation, in conjunction with several other histone modifications, induces changes to the distribution of H3K79 methylation states in the cell, representing a novel DNA damage-induced trans-histone "crosstalk" pathway. In turn, these induced changes in H3K79 methylation states serve to regulate and coordinate specific DNA damage response and repair pathways. We plan to conduct a series of experiments to test this model, evaluating the proposed UV-induced trans-histone modification pathway, and examining several specific DNA repair pathways to determine the manner by which specific H3K79 methylation states influence these processes. These experiments will provide important insights into the relationship between histone modifications and DNA repair, and will invaluable for directing future work in this field. Given the conservation of histone modifications and DNA repair processes between yeast and humans, the results from this work will likely have implications for human health and cancer research, fitting the missions of the National Institute of General Medical Sciences and the National Cancer Institute. The proposed experiments will be conducted at a small undergraduate liberal arts institution, making this proposal highly appropriate for the Academic Research Enhancement Award (R15) program. Funding of this proposal will be used in part to provide research opportunities for undergraduate students, serving to encourage the pursuit of careers in biomedical research. PUBLIC HEALTH RELEVANCE: Damage to genetic information by environmental agents, such as ultraviolet radiation from sunlight, poses a serious risk to the survival of living organisms. While repair systems exist to rectify DNA damage, dysfunction of these systems can give rise to a wide range of clinical problems, including DNA damage sensitivity disorders and cancer. The proposal outlined in this application examines the role by which DNA packaging proteins, known as histones, participate in DNA repair. Histone proteins influence a broad array of cellular functions, and misregulation of these proteins is associated with diverse clinical issues, including cancer. From these studies, we will gain a greater understanding of how histones participate in the response to DNA damage, potentially revealing new therapeutic targets to treat related human health problems. Relevance to Undergraduate Education: In addition to the potential clinical benefits from this research project, this proposal has been designed to provide a variety of research opportunities for undergraduate students. Funds from this grant will be used to support two students to work in the Thompson laboratory during each of the three summers covered by this award, as well as one additional student per summer to work in the laboratories of Dr. Karolin Luger and Dr. Jessica Prenni at Colorado State University, where select experiments pertaining to this project will be executed. Funds will also enable students to attend and present their work at professional research conferences. Such experiences will inspire students to pursue graduate/professional studies in biomedical research, in addition to the contributions that these students will make towards the scientific goals of this project.